1. Field of the Invention
The present invention relates to a test of an electrostatic breakdown of a semiconductor device and, more particularly, to a test method of an electrostatic breakdown and an apparatus adapted for causing in a simulated manner an electrostatic breakdown of a semiconductor device in a real-use condition.
2. Description of the Prior Art
Static electricity is generally generated when different members are brought in contact with or removed away from each other while friction occurs therebetween. This static electricity affects a semiconductor device in various ways. The semiconductor device is affected by, for example, static electricity generated during transportation of the semiconductor device or static electricity existing in environments in which the semiconductor device is used. As a result, an electrostatic breakdown is caused in the semiconductor device with relative ease because of a fine structure thereof. More particularly, this trend becomes noticeable because of a low resistance of the electrostatic breakdown in a MOS (Metal Oxide Semicondcutor) type semiconductor integrated circuit device (hereinafter referred to as "MOSIC") due to a high input impedance and also because of a large-scale integration of MOSIC.
In MOSIC, this breakdown of an oxide film by the static electricity causes trouble because a thin gate oxide film is directly connected to input terminals. Therefore, in such a semiconductor device, this thin gate oxide film is protected using an input protection circuit. This input protection circuit serves to immediately absorb the static electricity so that a high voltage may not be applied on the thin gate oxide gate film. However, the input circuit could be broken down by the absorption current caused on that occasion. A typical example of the breakdown due to the static electricity in MOSIC is a breakdown of the thin gate oxide film in the input circuit.
As a test method of causing an electrostatic breakdown to occur in a real-use condition in a well simulated manner, a "new ESD(Electrostatic Discharge) test method" is disclosed by Y. Sato et al. of Mitsubishi Denki Kabushiki Kaisha in ISTFA(International Symposium for Testing and Failure Analysis) in 1986. FIG. 1 is a schematic perspective view showing one example of a tube vibration type testing apparatus employed in this test method of an electrostatic breakdown. This testing apparatus comprises a carriage case 22 made of plastic in which a plurality of semiconductor devices 1 are placed, a carriage case supporting material 23 on which the carriage case 22 is mounted, and a vibrating apparatus 24 for vibrating the carriage case supporting material 23. As shown in FIG. 2, each semiconductor device 1 comprises a semiconductor chip 101, lead terminals 102 connected to the semiconductor chip 101, and packages 103a and 103b for protecting and securing them.
Operation of this tube vibration type testing apparatus is described. First, the plurality of semiconductor devices 1 are inserted in a row into the carriage case 22 which is a plastic tube having a U-shape cross section. The carriage case 22 in which the semiconductor devices 1 are contained is fixed to the supporting material 23. Thereafter, a vibrating axis 24a is turned in directions shown by arrows D and E within a predetermined angular range by the vibrating device 24. As a result, the supporting material 23 is vibrated in directions shown by arrows F and G. At the same time, the plurality of semiconductor devices 1 in the carriage case 22 are moved in frictional manner on an inner face 22a of the carriage case 22 while their adjacent end faces collide with each other. Static electricity is generated by this friction. This static electricity is discharged from the lead terminals 102 of the semiconductor device 1 to the semiconductor chip 101. Then, the thin gate oxide film in the input circuit of each semiconductor device is broken down. In this way, a phenomenon of the electrostatic breakdown in a real-use condition can be caused to occur in a simulated manner. The vibration is carried out by a predetermined number of times dependent on the amount of the static electricity. Therefore, the resistance to the electrostatic breakdown in the real-use condition can be relatively evaluated by the number of vibrations. Each semiconductor device 1 is taken out from the carriage case 22 after having been vibrated by the predetermined number of times. Then, various electrical characteristics are measured in a test for each lead terminal by a tester to determined whether the electrostatic breakdown has occurred. This test is generally employed as a breakdown test conducted in development of new semiconductor devices or a sampling test in mass production.
In the conventional test method, the semiconductor devices, which are inserted into the carriage case in a row as described above, collide with each other by means of vibration to discharge static electricity. Thus, the static electricity is discharged only at the lead terminals 102a, 102b, 102c and 102d of the end portions of each semiconductor device 1 shown in FIG. 2. As a result, the resistance to the electrostatic breakdown can be evaluated only on the lead terminals of the end portions.
Furthermore, in the semiconductor devices inserted into the carriage case and vibrated, a breakdown phenomenon by the static electricity generated during transportation is only simulated.